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Lec 16
Transgenic Plant technology- Applications
 Plants obtained by transfer of foreign genes to plant cells through vectors or direct
gene transfer methods.
 The next 20yrs of biotechnology are expected to improve quality of life through
improved crops, foods, pharmaceuticals, new industrial materials and a better
environment.
Transgenic plants were first created in the early 1980s and research has developed
transgenic plants with commercially useful traits such as resistance to herbicides, insects,
and viruses.
Making a Transgenic Plant
Identifying a Desirable Gene
We know very little about the specific genes that determine plant characteristics.
Effort focused at sequencing and understanding the functions of genes in agriculturally
important plant species would accelerate this process immensely.
Modifying the Gene
To ensure that the gene is expressed (translated into protein product) at the right
place and time, a promoter sequence is added. Changing the sequence of the gene can also
optimize resultant protein function. Successful incorporation of the transgene is a rare event
in plants; therefore a marker gene (e.g. drug resistance) is usually added to allow selection
Transformation
 Gene Gun
 microprojectile bombardment or biolistics
 Gold particle coated with the DNA containing the gene of interest is shot into the
nucleus of a plant cell, the DNA will detach and may become incorporated into the
plant chromosomes.
 Agrobacterium Infection
Agrobacterium tumefaciens is a species of bacteria commonly found in soil. This
bacteria has the amazing ability to infect plant cells with a piece of its own DNA called T-
DNA. Upon infection, the T-DNA will integrate into the plant chromosome, takeovers the
plant's cellular machinery and uses it to produce more bacteria.
To use Agrobacterium as a mean to incorporate transgenes in plant chromosomes,
scientists have removed the tumor-causing genes on the T-DNA (disarmed), but left the
bacteria’s abilities to infect a plant and transfer its T-DNA intact. The plant cells are cultured
with Agrobacteria carrying the transgene. The recombinant DNA will be transferred to the
plant cell. Transformed cells have to be selected. Regeneration of the plant will be done and
the resultant is Genetically modified plant
Selection and Regeneration
After the plant cells are infected with Agrobacteria, they are transferred to a selective
media where cells that did not incorporate the transgene will die.
The cells, which harbor the transgene, are then regenerated in media containing
nutrients and growth hormones.
Testing the transgenic plant
Once a transgenic plant is obtained, a set of extensive tests has to be done. Every
transgenic plant must be verified for the incorporation of the transgene.
If the transgene is present, the plant is evaluated for any adverse effects imposed by
the transgene.
Assays are done to determine the activity of the transgene, whether this gene is
passed stably from one generation to the next, and whether there are unforeseen effects on
plant growth, yield, and quality. If a plant passes these tests, it is rarely directly used for crop
production, instead it will be crossed with an improved line of the crop.
Increase Yields
Crops can be modified to optimize growth conditions: improve nitrogen assimilation,
increase oxygen absorption, efficient photosynthetic pathway, and increase starch
biosynthesis.
Insect Resistance
Various insect resistant crops have been produced. Most of these make use of the
Cry gene in the bacteria Bacillus thuringiensis (Bt); this gene directs the production of a
protein that causes paralysis and death to many insects.
Herbicide resistance
Roundup Ready™ Soybeans
A problem in agriculture is the reduced growth of crops imposed by the presence of
unwanted weeds. Herbicides such as RoundupTM and Liberty LinkTM are able to kill a wide
range of weeds and have the advantage of breaking down easily. Development of herbicide
resistant crops allows the elimination of surrounding weeds without harm to the crops.
Golden Rice
Through the work of two European scientists, Dr. Ingo Potrykus of the Swiss Federal
Institute of Technology in Zurich and Dr. Peter Beyer of the University of Freiburg in
Germany, rice plants were developed containing two Daffodil genes and one bacterial gene
(Erwinia uredovora) which carry out the steps required for the production of beta-carotene in
rice endosperm. Endosperm is the nutritive tissue surrounding the embryo of a seed. The
resulting plants appear normal except that after milling (to remove the brown bran), their
grain is golden yellow color due to the presence of provitamin-A (Toenniessen 2000).
More than 120 million children in the world suffers from vitamin A deficiency. Golden
Rice has the potential to help prevent the 1 to 2 million deaths each year caused by a
deficiency in this vitamin.
Virus Resistant Crops
Papaya is always infected with the papaya ring spot virus. Virus resistance gene was
introduced. The Freedom II squash has a modified coat protein that confers resistance to
zucchini yellow mosaic virus and watermelon mosaic virus II.
Genetically modified plants have been used as “bioreactors” to produce therapeutic
proteins for more than a decade. A recent contribution by transgenic plants is the generation
of edible vaccines.
Edible vaccines are vaccines produced in plants that can be administered directly
through the ingestion of plant materials containing the vaccine. Eating the plant would then
confer immunity against diseases.
Edible vaccines produced by transgenic plants are attractive for many reasons. The
cost associated with the production of the vaccine is low, especially since the vaccine can be
ingested directly, and vaccine production can be rapidly up scaled should the need arises.
Edible vaccine is likely to reach more individuals in developing countries.
The first human clinical trial took place in 1997. Vaccine against the toxin from the
bacteria E.coli was produced in potato. Ingestion of this transgenic potato resulted in
satisfactory vaccinations and no adverse effects.
One focus of current vaccine effort is on hepatitis B, a virus responsible for causing
chromic liver disease. Transgenic tobacco and potatoes were engineered to express
hepatitis B virus vaccine. During the past two years, vaccines against a E.coli toxin, the
respiratory syncytial virus, measles virus, and the Norwalk virus have been successfully
expressed in plants and delivered orally. Researchers at the
University of Agricultural
Sciences in Bangalore have developed muskmelon plants with rabies vaccine genes.
GMO
 Any organism derived from the transgenic technology are called “ GMO’s
(Genetically modified organisms)
 Any food produced in this way is called ‘GM food’.
 Starting from the Flavr-savr tomato with an extended shelf life, produced in 1994, a
number of transgenic crops have been marketed.
Why to Produce GM Food?
 From economical and agricultural standpoints, it is advantageous to grow crops that
have higher yield or improved quality, pest or disease resistance, or tolerance to
heat, cold and drought. Desirable genes may provide means for plants to combat
these conditions.
 Traditionally, combining the desirable genes in one plant is a long and laborious
process, involving crossing one plant to another plant of the same species or related
species.
 The development of transgenic technology allows useful genes from various living
sources to be brought together in a relatively simple manner.
Advantages of GM Food
 Increase crop yields, e.g. increase the size and number of seed
 Improve sensory attributes of food, e.g. flavor, texture
 Increase the nutritional value of crops, e.g. increase the protein content of rice
 Increase tolerance to adverse growing conditions, e.g. cold/heat/drought
 Provide resistance to pests and reduce the use of pesticides
 Selectively reduce allergy-causing properties of some foods
 The United Nations estimated that with the world population reaching 7.15 billion by
2015, 575 million people will face chronic malnutrition and famine.
 By increasing crop production and nutrient composition, GM food has the potential to
reduce hunger, malnutrition, and perhaps alleviates poverty
Concerns of GM Food
In the United States, where GM crops are most abundant, they are regulated by
three federal agencies: the Environmental Protection Agency, the Food and Drug
Administration, and the United States Department of Agriculture. The assessments, including
that performed by the manufacturers, may take several years to complete, and the GM food
is only released into the market when it meets all the requirements set out by these
agencies.
In Canada and the United States, labeling of GM foods is only required when the
food is significantly different from its conventional counterpart in composition, nutrition and
allergenicity.
References
Ye, X., S. Al-Babili, A. Kli, J. Zhang, P. Lucca, P. Beyer, and I. Potrykus. 2000. Engineering
the provitamin A (-carotene) biosynthetic pathway into (carotenoid-free) rice
endosperm. Science 287:303-305.
Chargelegue D, Obregon P, Drake PM. Transgenic plants for vaccine production:
expectations and limitations. Trends Plant Sci. 2001 Nov;6(11):495-6.
Daniell H, Streatfield SJ, Wycoff K.Medical molecular farming: production of antibodies,
biopharmaceuticals and edible vaccines in plants. Trends Plant Sci. 2001
May;6(5):219-26.
Richter LJ, Thanavala Y, Arntzen CJ, Mason HS. Production of hepatitis B surface antigen in
transgenic plants for oral immunization. Nat Biotechnol. 2000 Nov;18(11):1167-71.
Moellenbeck, D.J., M.L. Peters, J.W. Bing, L.S. Higgins, L. Sims, et al. 2001. Insecticidal
proteins from Bacillus thuringiensis protect corn from corn rootworms. Nature
Biotechnology 19:668-672.
Guerinot, M.L. 2000. Enhanced: the green revolution strikes gold. 2000. Science 287:241243.
Resources on the Web
Transgenic Crops: and introductory and resource guide-very comprehesive web site on
transgenic plants
http://www.colostate.edu/programs/lifesciences/TransgenicCrops/index.html UC Davis
Biotechnology Program-has a series of PowerPoint presentations on transgenic plant
http://www.biotech.ucdavis.edu/
Colorado Agricultural Information http://www.csuag.com/
Environmental News Network GM Food Information-contains introduction to GM food and a
quiz on the topic http://enn.com/indepth/gmfood/index.asp
DNA for Dinner http://www.gis.net/~peacewp/webquest.htm#Introduction
Food for Our Future http://www.foodfuture.org.uk/
Saskatchewan Agricultural Biotechnology Information Centre Agrobacterium animation:
http://www.agwest.sk.ca/sabic_index_tp.shtml
University of Nebraska gene gun animation: http://croptechnology.unl.edu/